tiny-pattern-ts/AGENTS.md

AGENTS.md

Machine entry point for AI coding agents working in this repo. The authoritative guidance for humans lives in CONTRIBUTING.md and README.md; this file only points at it and states the stable first-action facts. Do not restate evolving prose here — it will drift.

First action

• Project: F#-style pattern matching for TypeScript/ESM. Node >=26 (pinned via .node-version), ESM-only (no CommonJS shim).

• While iterating: npm run test (check:tsc + the unit suite) for fast feedback on the files you changed.

• Optional code intelligence: this repo installs @spences10/pi-lsp (pinned in .pi/settings.json) as a project-local pi extension. It talks to the repo's own TypeScript 7 via tsc --lsp --stdio and exposes read-only tools — lsp_hover, lsp_definition, lsp_references, lsp_find_symbol, lsp_document_symbols, lsp_diagnostics(_many). Prefer lsp_references over grep -w for widely-colliding identifiers (matches, type, …); use lsp_hover to read inferred types on generic-heavy code. It has no rename / code-action / apply-edit surface — the write side is pi's edit tool + check:tsc. Treat empty LSP output as inconclusive, not success: npm run test / npm run verify remain the sole authoritative gate (see the next bullet). The server keeps running across that gate with a ~5 min idle timeout and registers no file watchers, so if you change tsconfig.json / package.json mid-session its diagnostics can be stale — when LSP output disagrees with check:tsc, trust check:tsc and restart pi (or wait out the idle timeout) before concluding the LSP is wrong.

• Definition of done — run this before you call the work finished: npm run verify. If all green, commit. If red, look at the output, fix the root cause, and re-run.

• On commit: write a good message (see CONTRIBUTING.md § Commit messages). Lefthook's pre-commit hook already runs the fast, offline, staged-file checks — don't run them by hand. If the hook fails on style, npm run fix, restage, recommit.

• npm run maintain is NOT part of the feature loop. Its scans are advisory, never a gate; run them only on an explicit maintenance / update-deps branch.

  npm run test    # while iterating (fast feedback)
  npm run verify  # definition of done: whole-project correctness, one shot
  

Never do

Don't silence the type system to force a green run. As an agent these are forbidden:

• // @ts-nocheck, // @ts-ignore, // @ts-expect-error
• // oxlint-disable / // oxlint-disable-next-line
• as casts used to push an expression through (type-aware oxlint already flags unsafe assertions)

Fix the root cause with the type system instead — narrowing, generics, satisfies, conditional / mapped types, utility types (NonNullable, Exclude, …). TypeScript can express it; that's the intended tool. The oxlint-disable-location rule in CONTRIBUTING.md § Rules the tools don't enforce is a human last-resort convention (so a reviewer can spot a deliberate suppression) — it is not permission for you to add one. If the types genuinely cannot express something, stop and surface the conflict (commit message / handover) rather than suppress it.

The same applies to the checks themselves: never git commit --no-verify (or otherwise skip a pre-commit / pre-push hook). The checks are fast and offline, so a redundant run is fine — bypassing a hook to get green is the identical anti-pattern. If a commit already skipped a hook, redo it through one: git reset --soft HEAD~1 && git commit -C <skipped-sha>.

Never start a long-lived / blocking process such as npm run watch. It runs until a human stops it with Ctrl-C, so in an agent turn it hangs forever and floods the context with continuous output. Reach for a one-shot command instead — npm run test (or npm run check) — to get feedback.

Backlog

backlog.tasks uses the vscode-todotasks format (not Markdown). A line ending in : is a project; every other line is a task. Status glyphs: ☐ open, ✔ done, ✘ cancelled; subtasks nest by indentation. Inline @tags carry metadata — @done / @cancelled mark completion, @critical / @high / @low / @today set priority. The (…) timestamp after @done is editor-generated: omit it when checking off by hand.

Required coupling: a ✔ line must also carry @done, and a ✘ line must carry @cancelled. The sandy081.todotasks extension treats the glyph as the completion signal, then unconditionally searches for the matching tag to decorate; a bare ✔/✘ with no tag makes it compute an illegal Range (negative character offset) that throws and kills all highlighting/decoration for the document. A ☐ may stand alone. So check off by hand as ✔ … @done (optionally @done (timestamp)), never a lone ✔.

Working on tasks

• Task with subtasks (a task that has indented children): create the branch with npm run create:branch -- <prefix>/<desc>, inferring the prefix from the task content (feature/… / fix/… / chore/…) — do not hand-write git switch -c, the command enforces the clean-tree / current-main / green-baseline precondition. Work on each subtask with commits, then present a concise handover for the user to review. Use this fixed shape:

  ## Handover — <branch>
  
  **Implemented:** <what was built, and how>
  **Judgement calls:** <where the task was unclear, and what you assumed>
  **Known problems:** <open issues, caveats, follow-ups>
  

  Once the user has no further objections, merge back: git checkout main && git merge --no-ff <branch>. The branching model is documented in CONTRIBUTING.md § Branching model.

• Leaf task (no indented children): implement on the current branch and commit.

In both cases, follow CONTRIBUTING.md § Testing discipline (type-driven). Each subtask gets one or more commits.

Read these

• CONTRIBUTING.md § Rules the tools don't enforce — the constraints the linters don't catch; CI/review bounce these. The most important section.
• CONTRIBUTING.md § Testing discipline (type-driven) — write the expectTypeOf (type) before the assert (red); the types are the feature.
• CONTRIBUTING.md § Script prefix convention — adding an npm run script? reuse an existing prefix or it doesn't belong.
• CONTRIBUTING.md § Commit messages — gitmoji + imperative + 50/72.
• CONTRIBUTING.md § Feedback tiers — what runs when and at what cost (watch / pre-commit / pre-push / check / verify / fix / maintain / CI).
• README.md § Tooling decisions — the rationale behind each tool choice; read before changing tooling.
• package.json #scripts — the source of truth for every command (the LEFTHOOK_FILES convention scopes them to staged files vs. the whole project).